- add #ifdef to enable building ScaffoldNetwork with no Boost serialization support (#3538)

- do not look for Threads if not needed

CMakeLists.txt

@@ -367,9 +367,9 @@ if(RDK_BUILD_DESCRIPTORS3D)
 endif(RDK_BUILD_DESCRIPTORS3D)
 
 
-find_package (Threads)
-set(RDKit_THREAD_LIBS Threads::Threads)
 if(RDK_BUILD_THREADSAFE_SSS)
+  find_package (Threads)
+  set(RDKit_THREAD_LIBS Threads::Threads)
   target_compile_definitions(rdkit_base INTERFACE -DRDK_THREADSAFE_SSS)
   if(RDK_TEST_MULTITHREADED)
     target_compile_definitions(rdkit_base INTERFACE "-DRDK_TEST_MULTITHREADED")

Code/GraphMol/ScaffoldNetwork/ScaffoldNetwork.h

@@ -192,4 +192,5 @@ struct version<RDKit::ScaffoldNetwork::ScaffoldNetwork> {
 }  // namespace serialization
 }  // namespace boost
 #endif
+
 #endif